JPS61249067A - Copying machine - Google Patents

Abstract

PURPOSE:To obtain copy images which differ in image reproducibility with good response by switching selectively plural developing devices which are provided at the periphery of an electrostatic latent image carrier and charged with developers differing in toner density, and developing images. CONSTITUTION:The 1st and the 2nd developing devices 10 and 20 develop an electrostatic latent image formed on the surface of a photosensitive drum 1 which is driven to rotate as shown by an arrow (a) and those developing devices 10 and 20 has magnetic brush type structure and are different only in toner density between their internal developers. The surface of the drum 1 is exposed firstly to a negative image charged electrostatically to, for example, -600V to form an electrostatic latent image and a developing bias of, for example, -500V is applied to either of sleeves 11 and 21 of the developing devices 10 and 20 to stick negatively charged toner on image parts of the electrostatic latent image, thereby forming a positive developed image.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a copying machine that obtains copied images using an electrophotographic process.

In general, copying machines, such as microfilm reader printers, are required to have good line drawing reproducibility and halftone reproducibility.

In order to satisfy these conflicting demands, a copying machine has been proposed in which the gradation reproducibility of a copied image can be arbitrarily changed (see Japanese Patent Laid-Open No. 58-217950).
. In this publication, methods for changing the gradation reproducibility of a developed image include (a) a method of changing the charged potential of the photoreceptor and the image exposure light amount, (b) a method of changing the toner concentration of the developer, and (c) a method of developing. A method of changing the bias potential and the image exposure light amount is disclosed.

However, in the methods (a) and (c) above, 2
Since there are various types of changing elements, control becomes complicated, which is not desirable. Furthermore, the method (b) requires only one change element, and although it can be said to be preferable in this respect, it has the problem of poor responsiveness.

That is, as disclosed in the above-mentioned publication, it is difficult to immediately change the toner density in one developing device. For example, concentration a? If it is a change in the direction of the drop, adding toner is sufficient (even in this case, it is difficult to say that the density will increase immediately),
If the change is to decrease the density, it is necessary to wait until the toner is consumed by development.

An object of the present invention is to provide a copying machine that can instantly change the image reproducibility such as the gradation of a copied image. It also includes changing a wide range of other elements.

Means for Solving the Problems Therefore, the copying machine according to the present invention arranges a plurality of developing devices around the electrostatic latent image carrier, and selectively switches each developing device to perform development. The present invention is characterized in that a copy image with good image reproducibility is obtained.

Figures 1 and 2 show the main parts of an embodiment of a copying machine according to the present invention, in which a first developing device (io) and a second developing device (20) are installed in two stacks. , electrostatic latent images formed on the surface of the photoreceptor drum (1) rotated in the directions of the arrows (,) can be developed.

Both the first developing device (10) and the second developing device (20) have the same configuration of magnetic brush type, and differ only in the toner concentration of the developer contained therein. - That is, each developing device (10), (20) has a developing sleeve (11), (21) facing the photoreceptor drum (1), respectively, and inside the developing sleeve (11), (21), A magnetic roller (12L (22)) magnetized with N and S poles is built into the outer periphery, and the developer is applied to the outer periphery of the developing sleeves (11) and (21) by the magnetic force of the magnetic rollers (12) and (22). While being attracted, the developing sleeve (11) is rotated in the direction of arrow (b) of the developing sleeves (11) and (21).

(21) is conveyed on the outer peripheral surface in the direction of arrow (b).

Note that the amount of conveyance is regulated when the developer passes through the height regulating plates (13) and (23).

The developer is made of a mixture of a magnetic carrier and a toner, specifically a mixture of a small-diameter binder-type magnetic carrier and a non-magnetic insulating toner, and the magnetic carrier is charged positively and the toner is charged negatively by frictional charging. However, the toner concentration of the developer in the first developing device (10) is set to 8 wt%, and the toner concentration of the developer in the second developing device (20) is set to 12 (2) t%.

Behind the developing sleeves (11) and (21), there is a partition wall (
19), (29) and the developer circulation passage (14a) = (14b), (2
4a)=(24b) are formed, and passages (14a) and (2
In 4a), screw rollers (15) and (25) are indicated by arrows (
c), the passage (14b), (2
4b) has a packet roller (16L (26)) pointing at the arrow (
The developer is installed so that it can be rotated in the direction of
6').

passages (14a) and (14b) based on the rotation of (26);
, (24a), and (24b) are circulated.

Toner is stored in a toner bottle (not shown) for each developing device (10), (2o), and is replenished to the front side of the path (14a)=(24a) based on a toner replenishment signal. The replenished toner mixes with the developer, is mixed and agitated by the rotation of the screw rollers (15) and (2!5), and is conveyed to the inner side through the passages (14a) and (24a), and during this conveyance, negative charged. The developer passes through the passage (14a), (
Passage (14t+), (24b) 1” on the back side of 24a)
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%6-Tan (1G)-(9n ■-4@Adjacent developing sleeve (11) being conveyed to the front side.

It is supplied to the outer peripheral surface of (21).

On the other hand, each developing device (10), (20) has a frame (30).
.

(31), is pressed to the right by a cam plate (33) that presses against the frame (30), and is regulated in position by the frame (32) coming into contact with the cam plate (35). ing. The cam plate (35) is rotatable by a moving means (not shown), and has two positions: a position where the small diameter part contacts the frame (32) (see Figure 1), and a position where the large diameter part contacts the frame (32) (see Figure 2). ). In addition, a developing device (1
0) and (20) are rotatably supported in the vertical direction about the support shaft (34) of the cam plate (33), and when the small diameter portion of the cam plate (35) abuts the frame (32), the developing Vessel (10
) and (20) are located approximately horizontally, the developing sleeve (11) is close to the surface of the photoreceptor drum (1), and the developing sleeve (21) is separated from the surface of the photosensitive drum (1). Development is possible. On the contrary, 1. When the large diameter portion of the cam plate (35) comes into contact with the frame (33), the developing devices (10), (20)
rotates slightly upward about the support shaft (34), and the developing sleeve (21)
The developing sleeve (11) is moved away from the developing sleeve (11), and development can be performed in the second developing device (20).

By the way, this embodiment is a reader printer which obtains a positive copy image from a microfilm which is a negative original, and the development is performed using a reversal development method.

That is, the surface of the photoreceptor drum (1) has a direction of rotation [arrow (
a)] On the upstream side, first, after being charged to -600 Vi, the negative image is exposed to form a negative electrostatic latent image, which is selectively developed by one of the developing devices (10) and (20). Perform development. During development, any selected developer (10)
, (20) developing sleeve (11).

A developing bias of -500V is applied to (21), and negatively charged toner adheres to the image area of the electrostatic latent image, forming a positive developed image. This developed image is transferred onto copy paper by a positive discharge from a transfer charger (not shown) installed on the downstream side in the direction of arrow (a).

Switching between the developing devices (10) and (20) used for development is performed by operating a changeover switch on an operation panel (not shown). Based on this changeover signal, the cam plate (35) rotates, and the first When the developing device (10) is selected, as shown in FIG.
) is brought close to the photoreceptor drum (1), and the second developing device (2
0), as shown in FIG. 2, the large diameter portion of the cam plate (35) comes into contact with the frame (32) to bring the developing sleeve (21) close to the photosensitive drum (1).

In addition, a developing device (10) or (20) not used for development
In this case, the screw roller (15) or (25) and the packet roller (16) or (26) are rotationally driven to continue the circulation of the developer, but the rotation of the developing sleeve (11) or (21) is will be stopped.

In this way, the developing device (10) or (2
It is the developing device (10) or (20) that is not used for development that separates the developing sleeve (11) or (21) of 0) from the surface of the photoreceptor drum (1) and stops its rotation.
), and in particular, the developed image is scraped off by the developer on the developing sleeve (21) of the second developing device (20) during development in the first developing device (10). This is to prevent blurring of the image from occurring. Also, when developing with the second developing device (20), the first developing device (10
) to stop the rotation of the developing sleeve (11),
It is also desirable to prevent the red developer from scattering from the opening facing the photoreceptor of the first developing device (10).

As mentioned above, the toner concentration in the developer in each developing device (10) and (20) is 81% in the first developing device (10) and 12+IIt% in the second developing device (20). be. In order to maintain this toner concentration at all times, this embodiment is provided with a conventionally known toner replenishment control means. For example, A.T.
As abbreviated as DC, developing units (10), (20
) The toner concentration in the developer is directly detected using a magnetic sensor or the like, and this detected value is compared with a reference value, and when it is determined that the toner concentration is insufficient, toner is replenished.

Alternatively, as abbreviated as AIDC, a method may be used in which the toner density of a reference developed image formed on the surface of the photoreceptor is detected using a 7-photo sensor or the like, and this detected value is compared with a reference value. In these cases, the standard values are 8u+t% and 12%, respectively.
The toner density is set to u+L%. Other methods for detecting the toner concentration include a method of measuring the developing current and a method of optically measuring the color of the developer.

In the above embodiments, the present inventors et al.
Copying experiments were conducted using the developer (20) for soft-tone images and the second developing device (20) for high-tone images, and it was confirmed that stable copied images could be obtained in each case. Figure 3 shows the image reproduction characteristics obtained in this experiment, and in the low density region of the original, the second developing device (20) is more effective than the first developing device (10).
It is understood that a darker image can be obtained by using .

In other words, the first developing device (1
0) has good halftone reproducibility and toner density 12u+L%
It can be said that the second developing device (20) has good fine line reproducibility.

That is, in the above embodiment, two developing units (1, 0) and (20) having different toner densities are arranged side by side and the operation of each is selectively switched, thereby improving the gradation reproducibility of the copied image. The gradation reproducibility can be changed quickly and responsively by operating a changeover switch.

In the copying machine according to the present invention, the factors that change image reproducibility are not limited to toner density alone. For example, the developing bias may be changed for each developing device, the amount of developer conveyed to the developing area may be changed, or the composition of the developer itself may be changed. In addition, the developing device is divided into a device exclusively for developing the line image portion and a device exclusively for developing the area image portion, and when obtaining one copy image, the electrostatic latent image is formed by dividing into the line image portion and the area image portion, and each Developing may be performed using a dedicated device to obtain one copy image as a result.

Of course, it can be applied not only to reader printers, but also to regular development in regular copying machines.

Effects of the Invention As is clear from the above explanation, according to the present invention, a plurality of developing devices are arranged around the electrostatic latent image carrier, and each developing device is selectively switched to perform development. Copy images with different image reproducibility can be obtained with good responsiveness by simple control of switching the developing device used for development.

[Brief explanation of the drawing]

FIGS. 1 and 2 are sectional views of essential parts of an embodiment of a copying machine according to the present invention, and FIG. 3 is a graph showing changes in image density with respect to document density by this copying machine. (1)...Photosensitive drum, (10), (20)...
Developing device, (11), (21)...Developing sleeve, (1
2), (22)...magnetic roller, (33)...pressing cam plate, (34)...positioning cam plate. Patent applicant Minolta Camera Co., Ltd. Agent
Patent attorney Blue and white Mug Two idiots 11g1 Biting 0 1≦ Figure 3 Shoulder slash

Claims (1)

[Claims] 1. A plurality of developing devices are arranged around the electrostatic latent image carrier, and each developing device is selectively switched to perform development, thereby obtaining copied images with different image reproducibility. A copying machine characterized by: 2. The copying machine according to claim 1, wherein each of the developing devices is filled with developers having different toner concentrations.